Calcium (Ca2+) plays a central role in Biology as a universal messenger by allowing cells to efficiently respond to extracellular signals via modulation of its intracellular level. The permeability of cellular membranes for Ca2+ ions is therefore carefully regulated by membrane proteins called ion channels. The mounting of an efficient immune response also requires an extended period of intracellular Ca2+ elevation in immune cells such as lymphocytes. B-lymphocytes are the cells of the adaptive immune system that are responsible for the production of antibodies. The diversity of ion channels expressed in B lymphocytes is greater than originally anticipated, and includes molecules such as L-type CaV-channel variants that were originally assumed to be specific for so-called excitable cells, such as cardiac or neuronal cells. Although the presence of these L-type channels in B-cells is well established, their function remains to be elucidated. The aim of this proposal is to establish genetic model systems allowing us to investigate the role of individual members of the L-type channel family in the B-cell context. This includes the generation and functional characterization of B-cell lines lacking L-type channels that can subsequently be complemented with wildtype and mutant versions of the channels. We also plan to analyze the function of these molecules in vivo by studying the effect of B-cell restricted genomic deletion of L-type channels in an existing mouse model. Because the immune response is a very complex interplay of numerous cell types in multiple locations of the body, this in vivo model represents a complementary approach to the cell lines that will allow us to study the potential role of L-type channels in B-cell development and activation in the context of the complete organism. Public Health Relevance Statement: L-type Ca2+ channels are important therapeutic targets of a class of drugs that include verapamil and diltiazem, which are commonly used to treat conditions such as hypertension in patients. It has been shown in vitro that these drugs also inhibit the Ca2+-response of immune cells, although at higher concentrations than these applied therapeutically. This suggests that immune specific variants of these channels exist that are less sensitive towards these compounds. A promising avenue of immuno-modulatory drug development is therefore to design modified versions of these known channel inhibitors that would specifically bind and inhibit the immune system versions of L-type channels. To this aim, it is essential to identify the functional variants of these channels expressed in the immune context, and their precise role during immune response activation. Furthermore, these findings could also be beneficial to young patients suffering from rare complex genetic disorders affecting L-type channel function, and who are known to show symptoms consistent with immuno-deficiencies. This proposal will contribute to answering these important questions by investigating the role of these channels in B-lymphocytes.